Senya is just an ordinary boy who wanted to become an astronaut as a child. One day, suddenly, he is transported to another world after seeing something like a "tower" crossing the sky from his school's rooftop. There, he witnesses a ruined world where skyscrapers are connected by suspension bridges. Perplexed, Senya manages to see a girl standing on the roof of another building, as well as a masked man holding a bloody weapon in his hands...